In conventional overhead valve internal combustion engines, at least two valves reciprocate to provide intermittent communication between intake and exhaust manifolds and a combustion chamber. The valves include valve stems that are commonly disposed in valve stem guides, supporting axial motion in an engine component such as an engine head. Lubrication is provided to upper portions of the valve stems by a spray of lubricating oil within a valve cover disposed over the engine head or by gravity flow from an associated rocker arm. Oil flows by the force of gravity and may be encouraged by a pressure differential in the manifold versus crankcase pressure along a free upper end of the valve stem toward the manifolds and valve heads.
Valve guide seals located between the valve stem and the valve guide serve various purposes. First, they minimize engine oil consumption by restricting oil entry into the manifold and the combustion chamber. Second, they help to minimize exhaust particulates that contribute to pollution. Third, they are helpful in minimizing guide wear, which is of particular importance with diesel engines due to the nature of their operation.
The valve stem, valve guide, and valve guide seals are annularly wrapped by a helical compression valve spring that serves to bias the valve into a closed position. The longitudinal ends of the valve spring are restrained by flanges on corresponding valve stem seal retainers, valve spring retainers and/or spring seats, thereby maintaining proper alignment and position of the valve and valve spring. Typically, a flange on the valve stem seal retainer captures the lower end of the valve spring, but is not affixed to any other engine part. During engine operation, the valves are opened by transmitting drive forces from cams that are rotating in synchronism with the engine rotation to the stem ends of the valves via rocker arms.
As the valves are opened, the helical valve spring compresses, resulting in a rotational torque being exerted against the valve stem seal retainers or spring seats. This torque tends to cause the valve seal, the valve guide, the valve stem seal retainers and/or the valve stem (i.e. anything connected to the valve spring) to rotate slightly during each valve reciprocation. In most engines, valves are not designed to rotate, so the rotative torque applied by the compressed valve spring is undesirable. However, in some engines, especially those engines that use cruder fuels, the valves are specifically intended to rotate a precise amount with each reciprocation so that harmful deposits may be scrubbed from the valve and valve seat surfaces. Valve rotation in these types of engines is accomplished by precision valve rotators, which are designed to rotate the valve a predetermined amount for each actuation of the valve. However, the rotative torque applied by the compressed valve spring during each actuation causes either more or less valve rotation than intended, thereby impacting the efficiency of the valve scrubbing process. It is therefore desirable to limit the rotative force component caused by compressed valve springs to more closely control the valve rotation.